Temperature compensated voltage regulator



y 1951 E. KEONJIAN 2,983,863

TEMPERATURE COMPENSATED VOLTAGE REGULATOR Filed Aug. 15, 1955 F|G.l.

||- SOURCE 2 LOAD mm 2? /RESULTANT 25'c.-5oc. 3 2a a /REF. DIODE soc.uJO o n: -o.3v.f 29 REF. DIODE 250.

9 REVERSE cURRENTm mA 2 3 4 5 s 7 a 9 c 4D|ODES 25 c. 123 & 3p 2?. K? 14mooss 60C. -o.3v. coo l-L 2 3 4 5 6 7 B 9 FORWARD CURRENT m mA FIG.4.

SOURCE LOAD l INVENTORI EDWARD KEONJlAN,

HIS ATTORNEY.

United States 2,983,333 Patented May 9, 1961 TEMPERATURE COMPENSATEDVOLTAGE REGULATOR Edward Keonjian, Syracuse, N.Y., assignor to GeneralElectric Company, a corporation of New York Filed Aug. 15,1955, SerrNo.$28,172

11 Claims. (Cl. '323-69) The present invention relates to voltageregulators and has as an object thereof to provide an improved voltageregulator wherein the output voltage is insensitive to changes inambient temperature.

The present invention provides a solution to the temperature instabilityproblem which arises with several types of voltage regulators. In asimple shunt type regulator in which the shunted current flows through avoltage reference device, the output voltage is often found to depend onthe ambient temperature. The dependence of the output voltage ontemperature is due to a change in the conductivity of the voltagereference device With changing temperature. Voltage reference deviceswhich are sensitive to ambient temperature are semi-conductor diodes ofgermanium or silicon which are operated in the inverse voltagebreak-down region and gaseous discharge devices. The invention isgenerally applicable to regulators in which an increase in the ambienttemperature brings about an increase in the voltage developed across thereference device.

The invention provides a voltage regulator temperature compensatingcircuit that is simpler than previously known arrangements, and onewhich avoids the disadvantages which have hitherto prevented the use ofsimple arrangements. The novel temperature compensating circuit heretreated provides excellent temperature stability while causing a minimumreduction in regulation and requiring a minimum source voltage toproduce a given regulated voltage output.

The compensation circuit further is capable of functioning not only inlow voltage and low current ranges but also in high voltage and highcurrent ranges. It is applicable to germanium or silicon diodes havingbreakdown voltages well below volts as well as to the more commonoperating voltages of gas discharge tubes. Furthermore, the compensatingcircuit can be used with voltage reference devices which operate atcurrents of less than a milliampere without substantial impairment f thevoltage-current or regulation characteristic of the compensatingnetwork. With larger compensating junction diodes, the range of currentsin which temperature compensation can be affected extends to severalamperes, permitting application of the invention to regulators employingsaturable reactors.

Accordingly, it is a further object of the present invention to providea temperature stabilized regulator wherein the regulation efficiency ofthe stabilization circuit is substantially undiminished.

It is still another object of the present invention to provide atemperature compensated voltage regulator capable of stabilizingrelatively low output voltages.

These and other objects of the present invention are achieved in a novelvoltage regulator circuit employing a voltage reference deviceexhibiting a positive voltagetempera'ture coefiicient and a temperaturecompensating network connected in series with it. In accordance with theinvention, one or more series connected semi-conductor diodes arrangedto conduct in the forward direction form a portion of the compensatingnetwork. Since the forward resistance of these diodes diminishes withtemperature the connection of a suitable number of properly selecteddiodes in circuit with a voltage reference source can be used to bringabout substantially perfect temperature compensation of the voltagereference source. The illustrative embodiments of the invention employrespectively a semi-conductor diode operated at a large enough inversevoltage to cause break-down as one such reference and a gaseousdischarge device as another. In these embodiments very little decreasein the regulation efiiciency is occasioned by the addition of thecompensation 7 network.

The features of the invention which are believed to be novel areset'forth with particularity in the appended claims. The inventionitself, however, both to its organization and method of operationtogether with further objects and advantages thereof may be bestunderstood by reference to the following description read in connectionwith the following drawings wherein:

Fig. 1 shows a schematic diagram of a temperature stabilized voltageregulator employing a reversely poled semi-conductor diode as thereference source;

Fig. 2 is a graph illustrating the conductive properties of p a typicalsemi-conductor diode operated from the region of inverse voltagebreak-down to the region of forward saturation;

Fig. 3 is a graph illustrating respectively the separate voltage-currentcharacteristics of the reference device and of the temperaturecompensating device of the embodiment illustrated in Fig. 1, in additionto the composite voltage-current characteristic of this embodimentillustrating the resultant temperature stabilization achieved; and

Fig. 4 is a second embodiment of the invention employing a gaseousdischarge device as the voltage reference source.

Referring now to Fig. 1, there is shown a voltage regulator embodyingthe present invention. A source 11 of direct potential has its negativeterminal 12 connected to a ground bus 13 and its positive terminal 14connected to a regulating resistance 15. The load 16 is connectedbetween the terminal 15 of the regulating resistance remote from thesource 11 and the ground bus 13. A voltage reference diode is shown at17 having its cathode connected to the ground bus 13 and its anodeconnected to one terminal of a temperature compensating network 18. Thetemperature compensating network 18 is connected in series between theload side of the compensating resistance 15 and positively energizedterminal of the diode reference device 17. By this poling of the diode,the source 11 tends to force current through the reference diode 17 witha sense opposite its direction of easy flow. The compensating networkcomprises four series connected diodes 19, 2t), 21, and 22 chosen sothat their temperature coefiicients bring about substantially completestabilization of the reference voltage appearing across the load 16.

In the constructive embodiment illustrated, the reference diode 17 is asilicon junction diode constructed to have an inverse break-down voltageof approximately 9 volts. The compensating diodes 19, 2t), 21 and 22 areeach germanium diodes.

In accordance with the invention it has been determined that byselection of an appropriate number of forward conducting semi-conductordiodes, connected in series with a reversely biased diode, one mayobtain essentially perfect temperature compensation of the outputvoltage. Since the forward conduction temperature coefiicient is usuallysmaller than the backward temperature coefiicient, this number isusually larger than one.

The method of achieving temperature compensation may be explained byreference to Fig. 2 on which is plotted the voltage-currentcharacteristics of a typical semi-conductor diode. The line 23 whichcorresponds to operation at a temperature of 25 is distinct from asimilar line 24 taken at 60". It may be noted, however, that except inthe vicinity of zero applied voltage, that the lines are closely similarin shape and are merely translations of one another along one axis ofthe graph. It may also be noted that at an arbitrary inverse currentpoint 25 on the graph, that the voltage corresponding to the 25 point isalgebraically greater than the voltage corresponding to the 60 point.Likewise, picking an arbitrary forward current at point 26 of equalmagnitude to the current of 25 but of opposite sign, it may be seen thatthe voltage corresponding to the line for 25 temperature isalgebraically more than the voltage corre sponding to the 60temperature. A careful study of the conduction properties of typicalsemi-conductor diodes indicates that the voltage-temperature coeflicientfor conduction in the forward direction and in the reverse direction arenot the same, and that they are ofopposite sign, and essentially linearover a wide range of operating conditions. Accordingly, by selection ofa sufficient number of forward conducting diodes one may achievesubstantially perfect temperature compensation of an inversely operatedreference diode.

Fig. 3 illustrates in detail the operation of the temperaturecompensated voltage regulator illustrated in Fig. 1. Fig. 3 containsfive separate curves of voltage versus current. Curve 27 illustrates theresultant curve of the compensated regulator shown in Fig. 1 over therange of from 25 to 60 C. taken across both the regulatingsemi-conductor 17 and the compensating semi-conductor 18. Curve 28represents the voltage characteristic taken across the reference diode17 alone at a 60 C. ambient temperature. Curve 29 represent the lattercharacteristic at 25 C. Curve 30 represents the voltage drop appearingacross four forward conducting germanium diodes (18) at 25 C. Curve 31represents the voltage drop in these diodes (18) at 60 C. At 2.4milliamperes, in the experimental embodiment illustrated in Fig. 1,approximately 0.3 volt difference was obtained between the referencediode voltages corresponding to the two temperatures and thecompensating diode voltages corresponding to the two temperatures. Atthe same time, the points corresponding to a temperature of 60 C. werefound to be nearly indistinguishable from the points obtained at 25 andhence were plotted as a single line 27. As measured, the voltage wasconstant to less than 0.01 volt over most of the graph through thistemperature range. The forward conduction curves are so nearly paralleland the reverse conduction curves are so nearly parallel throughout theillustrated range of from 1 to 9 milliamperes, that the compensation isexcellent throughout. The indicated reduction in regulation in thecompensated circuit is only approximately 35 volts per ampere over therange of from 0.6 milliampere to 9 milliamperes. If the range is changedto from 3.6 to 9 milliamperes, the decrease in regulation is 20 voltsper ampere.

Noting typical values, the voltage temperature coeflicient in thereverse conduction region for silicon diodes varies from approximatelyplus 0.01% per degree C. to plus 0.1% per degree C., the former valuecorresponding to a diode having a break-down potential in the region ofvolts and a dynamic resistance of approximately ohms in this region ofconduction. In general, the magnitude of the temperature coefiicient,the conductance, and the break-down voltage are interdependent, thediodes having the greater break-down voltage having the greater positivetemperature coefiicient.

The forward conduction characteristics of junction diodes can beexpressed by the equation:

=lse -1 (1) Where I is the saturation current, k a constant that at roomtemperature may vary between 30 volts and 20 volts depending on thedimensions of the diode, and v is the junction voltage. The factor k isproportional to the absolute temperature. This variation is so small,however, that it usually can be neglected.

The saturation current 1,, when a junction is biased forwardly, variesexponentially with temperature, being relatively independent of voltageover the intended operating range:

where I, is the saturation current at temperature T I the saturationcurrent at temperature T and 11" a constant. For most germanium andsilicon diodes, the coefiicient a equals approximately 0.08 (degrees K).

The total current-voltage characteristics is therefore:

In the forward part of the characteristic under the operating conditionscontemplated, the last term of (3) can be normally be neglected so that:

1=1 a('I T1)+irv 4 a 1 I zi ril-b 7:

For a constant current I, we have, therefore:

6V a w r (6) The voltage drop of a diode during forward conduction withconstant current changes, therefore, with temperature at a rate of -a/k.A typical value (for k=39 volts a=0.08 (degrees K)-' is 2 millivolts perdegree C. It is important to note that the temperature coefficient ofthe forwardly biased diode is always negative.

In general it may be said that the forward conduction temperaturecoefficients of germanium and silicon diodes are quite uniform, whilethe temperature coefficients for backward conduction diifer greatly withdifferent diodes. Since the positive temperature coefiicient goes upwith break-down voltage diodes operating at higher breakdown voltagesrequire a larger number of compensating diodes than diodes operating atlower break-down voltages. Since the temperature coefiicients forforward conduction are relatively uniform, it may be desirable in somecases to' employ shaping networks in order to achieve precisecompensation for a reference diode whose temperature coefficient wouldotherwise call for a fractional number of compensating diodes. A simpleshaping network may take the form of a resistance connected in shuntwith one or more of the compensating diodes. For most purposes, however,the use of the nearest number of compensating diodes brings aboutcompensation to an adequately high degree.

Fig. 4 illustrates another embodiment of the invention in which agaseous discharge device provides the voltage reference. A source ofdirect potential is shown at 32 having one terminal connected to aregulating resistance 33. A load 34 is connected to the terminal of theregulating resistance 33 remote from the source 32 and to the otherterminal of the source 32. The compensating voltage regulating circuitcomprises the gaseous discharge device 35 and the compensating network36, these elements being serially connected in shunt across the load 34.The compensating network 36 is formed of four forward conducting diodes37, 3'8, 39, and 40 whose total temperature coefficient is such as toprovide compensation of the positive temperature coeflicient of thegaseous discharge device 35. In this manner a typical gaseous dischargedevice, having a positive temperature coeflicient of 7.5 millivoltsper'de-gree can be compensated by four forward conducting diodes eachhaving approximately 1.9 millivolts per degree negative temperaturecoeflicient.

There are several types of diodes which exhibit the negative temperaturecoefficient forward conduction characteristic here employed. Silicon andgermanium junction diodes have been found to exhibit this property overan extremely wide range of currents. As is true in most junction diodes,the dynamic resistance decreases with increasing current levels, so thatthe reduction in regulation is greatest at the lower currents and aminimum at the higher currents. By appropriate design, diodes may bemade in which the knee of the resistance curve is below a milliampere,thus permitting high regulation when the compensating diode is operatedat currents above this point. The upper range of current operation islimited by the size of the diode, but in general the negativetemperature coefficient is exhibited throughout the normal current rangeof the diode.

While particular embodiments of this invention have been shown anddescribed it will of course be apparent that various modifications maybe made without depart ing from the invention. Therefore, by theappended claims, it is intended to cover all such changes andmodifications as fall within the true spirit and scope of the presentinvention.

What I claim as new and desire to Patent of the United States is:

1. In combination, a voltage reference device having a positivevoltage-temperature coefiicient and a compensating element having anegative voltage-temperature coefiicient of substantially equalmagnitude to said first recited coefiicient and connected in seriestherewith, said compensating element comprising a semi-conductor diodeoriented for easy conduction in the direction of normal current flowthrough said reference device.

2. A temperature stabilized voltage regulator comprising asemi-conductor diode adapted to be connected to potentials of suchmagnitude as to cause inverse breakdown of said diode, the voltage ofsaid breakdown having a positive temperature coefficient, and atemperature compensating element connected in series with said diode andcomprising a number of semi-conductor diodes arranged for easy currentflow in the direction of normal current flow through said referencesemi-conductor diode, said number being selected to provide a voltagedrop in said compensating element having a negative temperaturecoefficient of substantially equal magnitude to said positivetemperature coefiicient.

3. A temperature stabilized voltage regulator comprising a semiconductordiode adapted to be connected to potentials of such magnitude as tocause break-down of said diode, the voltage of said breakdown having apositive temperature coeiiicient, and a temperature compensating elementhaving a negative voltage-temperature coefficient of substantially equalmagnitude to said positive temperature coefficient, said compensatingelement being connected in series with said diode and comprising atleast one semi-conductor diode oriented for easy current flow in thedirection of normal current flow through said reference semi-conductordiode.

4. A temperature stabilized voltage regulator comprising a regulatingresistance adapted to be connected in series between a source ofenergizing potentials and a load device, and a voltage regulatingcircuit adapted to be connected in shunt with said load devicecomprising a constant voltage drop device having a positivevoltagetemperature coefficient and a temperature compensating elementhaving a negative voltage-temperature coefiicient or" substantiallyequal magnitude to said positive voltagetemperature coefiicient, saidcompensating element being connected in series with said constantvoltage drop device and comprising at least one semi-conductor diodeoriented secure by Letters 6 for easy current flow in the direction ofnormal current flow through said constant voltage drop device.

5. A temperature stabilized voltage regulator comprising a regulatingresistance adapted to be connected in series between a source ofenergizing potentials and a load device, and a voltage regulatingcircuit adapted to be connected in shunt with said load devicecomprising a semi-conductor diode adapted to operate in the inversebreak-down region, said semi-conductor diode having a positivevoltage-temperature coefiicient, and a temperature compensating elementhaving a negative voltage-temperature coeflicient of substantially equalmagnitude to said positive voltage-temperature coefiicient, saidcompensating element being connected in series with said diode andcomprising at least one semi-conductor diode oriented for easy currentflow in the direction of normal current flow through said inverselyoperated semi-conductor diode.

6. A temperature stabilized voltage regulator comprising a regulatingresistance adapted to be connected in series between a source ofenergizing potentials and a load device, and a voltage regulatingcircuit adapted to be connected in shunt with said load devicecomprising a semi-conductor diode connected for operation in the inversebreak-down region, said diode having a positive voltage-temperaturecoefiicient, and a temperature compensating element connected in serieswith said diode and comprising a number of semi-conductor diodes whoseforward resistance decreases with temperature, oriented for easy currentflow in the direction of normal current flow through said inverselyoperated semi-conductor diode, said number being chosen to make thetotal negative voltage-temperature coelficient of said compensatingelement substantially equal to the positive voltage-temperaturecoeflicient of said inversely operated device.

7. A temperature stabilized voltage regulator as set forth in claim 6wherein said temperature compensating diodes employ a semiconductormaterial selected from the class of materials including silicon andgermanium.

8. A constant voltage source comprising: a source of D.C. potential; aresistor; a pair of silicon diodes, a series circuit including saidsource of D.C. potential, said resistor and said pair of silicon diodeseach of said silicon diodes having a cathode and an anode electrodearranged in juxtaposition so that one electrode of one of said diodes isconnected to a like electrode of the other said diode, means to derive apotential across said pair of diodes.

9. In combination a reverse biased semiconductor diode voltage referencedevice, having a voltage temperature coefficient, and a compensatingelement, having a negative-voltage-temperature coeficient of oppositesense and of substantially equal magnitude to said first recitedcoeificient, connected in series therewith, said compensating elementincluding a semiconductor diode oriented for easy conduction in thedirection of normal current flow through said reference device.

10. Means for providing a temperature stabilized constant voltage sourcefrom a D.C. potential source, comprising a series circuit adapted to beconnected to said D.C. potential source and including a resistance, afirst semiconductor diode oriented for operation in the inversebreak-down region, said first diode having a first tem peraturecoefficient, and a second semiconductor diode oriented for easy currentflow in the direction of normal current flow through said inverselyoperated first diode, said second diode having a temperature coefficientof opposite sign to that of the temperature coeificient of said firstdiode, and means to derive a substantially constant D.C. potentialacross said diodes.

11. A temperature stabilized voltage source comprising a source of D.C.potential, a resistor, a first junction semiconductor diode, and asecond junction semiconductor diode, a series circuit including saidsource of DC. potential, said resistor, said first diode, and saidsecond diode, said first diode and said second diode being connected soas to be oppositely poled, said first diode exhibiting a positivevoltage temperature coefiicient and said second diode exhibiting anegative voltage temperature coefiicient, means to derive a temperaturestabilized constant potential across a portion of said series circuitincluding said first and said second diode. A

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 2 983 863 May9, 1961 EdwerdKeonjian It is hereby certified that error appears in theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 2 line 46 for cathode read anode same line 46 for anode readcathode column 4L,

line 23 strike out ioe fl first occurrence,

Signed and Sealed this 3rd day of July 1962o (SEAL) Attest;

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of PatentsUNITED STATES PATENT OFFICE CERTIFICATE. OF CORRECTION Patent Ne, 2,,98386s, May 9 1961 Edward I Keonjian It is hereby certified that errerappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as eerrected below.

Column 2 line 46 for cathode read anode 5 same line 46 fer Fanode"; readcathode column 4 line 23 strike eat be first oceumeenee.a

Signed and sealed this 3rd day of July 1962,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

